ewokracing i have heard 17 is a pretty good combo if you have the stock 43 on the rear also on your 04 sprint the speedo is connected to the front tire so changing sprockets doesn't affect it that's on the 1050s
36/42 f/r is what the book says; a lot of people like a little less than that, maybe 10% down. Don't know about machining discs; I gather that happens more often with non-floaters. You might try some copperslip or caliper grease on the back sides of the pads to get rid of the squeal.